This invention relates to a natural gas well effluent high pressure separator system of the type employed at a gas well head to remove connate well fluids from a well effluent composed of a mixture of gas, oil and water and, more particularly, to a self circulating gas jet driven heating system for use with such a natural gas high pressure separator.
Examples of gas separating and dehydrating units are disclosed in U.S. Pat. Nos. 3,094,574; 3,288,448; 4,342,572; 4,421,062 and U.S. patent application Ser. No. 661,398 filed Oct. 16, 1984 for FLUID PUMPING SYSTEM of Charles R. Gerlach and Rodney T. Heath now U.S. Pat. No. 4,588,424; the disclosures of which are specifically incorporated herein by reference. In general, such units comprise a separator means for receiving the gas-oil-water mixture from the well head and separating the oil and water liquids from "wet" (water vapor laden) gas; and a water absorber means, which employs a liquid dehydrating agent such as glycol, for removing the water vapor from the gas subsequent to its passage through the separator and producing "dry" gas suitable for commercial usage.
Such well gas dehydration units may comprise two separate glycol circulation systems, one glycol circulation system sometimes referred to as the glycol heating system circulates glycol through a closed loop between a heating means such as a reboiler and the separator means in order to maintain the temperature in the separator at an optimum value for separating oil and water mixture from the well effluent. Circulation of glycol in such a heating glycol circulation system is sometimes provided by a thermosyphon flow produced by the temperature difference between the separator and the reboiler. Another glycol circulation system, sometimes referred to as the process glycol circulation system, is generally caused to circulate by a glycol pump. The process glycol is continuously supplied to the absorber means in a "dry" low water vapor pressure condition and is removed from the absorber means in a "wet" high water vapor pressure condition. The wet glycol is continuously removed from the absorber means and circulated through a treater means which may include the reboiler means (which is also used to heat the heating glycol) and a still column, etc. for removing the absorbed water from the wet progess glycol to provide a new supply of dry process glycol. The glycol reboiler means usually comprises a gas burner for heating the glycol therein. Since the separating/dehydrating units are continuously operated at well sites without continuous monitoring by operating personnel, reliable continuous operation of the glycol circulation systems is of critical importance. Because of the often remote location of wells, it is highly desirable to use energy sources readily available at the well site for operation of these circulation systems. Since the glycol heating system uses substantial amounts of energy it is of upmost economic importance to operate this system with maximum efficiency and minimum energy loss.
Although the use of a thermosyphon, such as described in Heath, U.S. Pat. No. 4,342,572 to produce circulation in a heating glycol system is extremely energy efficient, a drawback of thermosyphon circulation is that it is relatively slow and thus limits the speed at which heat can be transferred to the separator by the heating glycol system.
Another manner of producing circulation in a heating glycol system is through use of a gas jet pump as described in U.S. Pat. No. 4,421,062 of Padilla Sr. which is hereby incorporated by reference for all that is disclosed therein. In this arrangement, well gas, after passing through a series of drip pots and regulators which reduces the gas pressure to about 25 psi, is injected into a heating glycol flow line which forms part of a closed loop system between a high pressure separator and a reboiler. The gas is injected through a nozzle structure directed toward the reboiler and induces a venturi effect on the glycol in the surrounding portion of the glycol flow line to produce upward flow thereof through a lift pipe portion of the flow line into the reboiler which consequently produces circulation of heating glycol from an opposite end of the reboiler into the separator. A relatively high circulation rate flow of heating glycol may be provided between the separator and the reboiler so long as gas is discharged through the gas nozzle structure. Gas flow to the gas nozzle structure is controlled by a thermostat in the separator which permits a gas flow through the gas nozzle structure whenever the separator temperature falls below a predetermined value and which shuts off the gas flow to terminate the circulation of heating glycol whenever the separator temperature exceeds another predetermined value. Gas discharged from the nozzle structure into the glycol flow is subsequently collected in a scrubber housing above the reboiler tank and is thereafter discharged through a gas outlet line having a relief valve set at approximately 23 psi. The gas outlet line from the scrubber passes through another series of check valves and is connected to the burner and burner pilot. The burner is turned on and off in response to a control signal from a thermostat in the reboiler. Thus, some of the gas discharged through the gas nozzle structure to produce circulation of heating glycol between the separator and reboiler is available for use by the burner and burner pilot. A problem with this system is that a great deal of the gas discharged through the gas jet may of necessity be vented to the atmosphere during periods when the gas jet is operating without the burner firing. Thus, this system may waste considerable amounts of gas. Another problem inherent in such a system is that there is no available means for removing heating glycol from the portion of the circulation line passing through the separator; thus, heat transfer to the separator from the heating glycol system cannot be rapidly terminated when needed for optimum separator temperature control.
It would be generally desirable to provide a heating glycol circulation system for circulating heating glycol between a reboiler and high pressure separator which provides the extremely high energy efficiency of a thermosyphon heating system while providing the relatively high speed circulation capability of a gas injection type circulation system without waste of valuable sale gas.
It would also be desirable to provide a heating glycol system which continuously circulates heating glycol to a separator when heat is required and which is adapted to enable evacuation of heating glycol from the circulation line portion passing through the separator to allow rapid temperature reduction in the separator when required.